SO. I walked up to the pat-down with the mask inside my hat, so when I removed it, I just held it away from the guy patting me down.

The girl looked at the sign and made an "Ehhhh I don't know" face. The other guy looks at it, smiles, and says, "I say let it go." I was stunned, and I thanked him twice.

List of Arrowhead personnel who cheered me on:

-Two drummers from the Rumble
-Fan assistance outside
-Guy who smiled at the sign and let me in
-Two fan assistants in the... I think H&R Block-sponsored booth or something. She was yelling and cheering and took a picture.
-Three important looking guys in suits smiled
-One security guard laughed

Another security guard told me, "That sign. You can't have that." I asked why not, and he didn't have an answer. He said, "If you hold it up again, I will escort you out." He came down to my seat 5 minutes later and said, "I got the okay. You can hold it up. Sorry about that."